2) Yes. However WooCommerce is not built into the theme. It’s still a third party plugin and you need to install it like a “normal” plugin. Flashlight comes with a php configuration file which takes care of the plugin integration.

3) See 2) – there’s no difference.

4) Flashlight is compatible with many (probably most) WooCommerce plugins but not with all. The reason is that Kriesi changes the default shop template structure a bit (with filters/actions, etc.) and this can affect third party plugins which rely on these filters/actions. It’s compatible with Subscriptions though. If you want to be sure that all WooCommerce extensions work with your theme rather buy http://themeforest.net/item/replete-ecommerce-and-business/3519946 because it’s a dedicated e-commerce theme and the WooCommerce integration is better (Flashlight on the other hand is more a photographer theme).